Fix failed migration so that support can revert resize

There are couple of scenarios in which the instance's vm_state and task_state are not in one of the allowed states. For instance the rsync process dies midway due to deployments or compute node restart and never goes to error state. In those cases support is forced to update the db and put the instance and migration to error status so that the revert goes through. The reset-state api only changes the vm state and marks the task state as None. We need to change the migration status to 'finished' for the revert.
We will have to add a new extension to reset the vm_state to 'resized', task state to None and the migration status to 'finished'